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Hebrew Birthday Calculator + Online Solver With Free Steps

The Hebrew Birthday Calculator determines the Jewish/Hebrew birthdate from a given Gregorian birthdate and the time of day relative to the sunset.

What Is the Hebrew Birthday Calculator?

The Hebrew Birthday Calculator is an online tool that converts a given Gregorian date into the equivalent Jewish/Hebrew date.

The calculator interface consists of two columns. The first column has three text boxes and the second column has three options, of which you must choose one. 

The first column deals with the birthdate and the three text boxes are labeled “DAY,” “MONTH,” and “YEAR.” Note that this birthdate must be according to the Gregorian calendar, so if you were born on September 18, 1985, you would enter 18 for the day, September for the month, and 1985 for the year. You can use abbreviations for months (Sep, Apr, etc.).

The second column determines the time of birth relative to the sunset. The three options are “After Sunset,” “Before Sunset,” and “Not Sure.” The sunset has the same significance in the Hebrew calendar as midnight in the Gregorian calendar as the Jewish day goes from sunset to sunset.

If Not Sure is selected here, the calculator assumes the time of birth to be before sunset.

How To Use the Hebrew Birthday Calculator

You can use the Hebrew Birthday Calculator to find someone’s Hebrew birthday by following the step-by-step guidelines below.

Step 1

Enter the date (1–31 except for Feb which is 1–28/29 during leap years) of birth into the first column’s text box labeled “DAY.”

Step 2

Enter the birth month into the first column’s second text box labeled “MONTH.”

Step 3

Enter the year of birth into the first column’s third text box labeled “YEAR.”

Step 4

Select the time of birth during the day relative to the sunset in the second column’s options.

Step 5

Press the Submit button to get the results.

Results

The result contains the Hebrew calendar date of the input Gregorian birthday.

How Does the Hebrew Birthday Calculator Work?

The Hebrew Birthday Calculator works by figuring out three essential things relating to the Hebrew calendar:

  1. When was Rosh Hashana during that Gregorian year? If the input Gregorian date is before Rosh Hashana for that year: Jewish Year = Gregorian Year + 3760, otherwise Greogiran Year + 3761.
  2. Was the Jewish year deficient/regular/complete?
  3. Was the Jewish year an intercalated/leap year

With this knowledge, it is possible to convert any Gregorian date to the equivalent Jewish date. The rules that define these characteristics are complex and not mentioned here.

If you do not have this information, you need a calendar. The calculator is handy here because it has access to the calendar data, leading to quick results.

Jewish Months

Because of the 13 months of the intercalated year, the Jewish month may fall on one of two Gregorian months. They are given below.

  1. Tishri, 30 (September/October – Jewish New Year, Rosh Hashana)
  2. Cheshvan, 29/30 (October/November)
  3. Kislev, 30/29 (November/December)
  4. Tevet, 29 (December/January)
  5. Shvat, 30 (January/February)
  6. Adar I, 30 (only in Jewish Leap Years)
  7. Adar / Adar II, 29 (February/March)
  8. Nisan, 30 (March/April – Spring, Passover holiday)
  9. Iyyar, 29 (April/May)
  10. Sivan, 30 (May/June)
  11. Tammuz, 29 (June/July)
  12. Av, 30 (July/August)
  13. Elul, 29 (August/September)

Lunisolar Nature of Jewish Calendar

The Jewish calendar is a lunisolar (based on both lunar and solar years) calendar, meaning that the average Jewish year length is almost equal to that of a solar year, despite being based on lunar phases.

The moon phases form the basis of the lunar cycle. The lunar cycle takes around 29.5 days, leading to alternating 30/29 day months for a 12-month lunar year. In contrast, a solar year is based on a full orbit of the Earth around the sun, which takes around 365 days. A lunar year is then around 354 days, almost 11 days less than a Gregorian year (365 days).

Additionally, the lunar phases recur on the same days of the year after almost 19 years. This is known as the Metonic cycle or machzor katan

Restrictions and Fixed Jewish Calendar

Since Passover is always held in the Spring season, the lunar cycle poses the problem that it would occur 10 days earlier every month, eventually occurring in different seasons.

Similarly, Hoshanah Rabba cannot occur on a Saturday, and Yom Kippur cannot fall on a Friday or Sunday. To ensure this, Rosh Hashana can only be on Monday, Tuesday, Thursday, and Saturday (4 gates). Occasionally, this requires postponing Rosh Hashana. 

These constraints allow the computation of a fixed Jewish calendar, which is used nowadays. 

Lunisolar Intuition

Converting to the lunisolar calendar requires periodically inserting an intercalated leap year. Every leap year, a 13th month Adar I (30 days) is added. Thus, a Jewish Leap Year (or intercalated year) has 13 months and occurs 7 times over the Metonic cycle. Specifically, years 3, 6, 8, 11, 14, 17, and 19 of the cycle are leap years. 

To compensate for Rosh Hashana postponements, a day is subtracted from Kislev’s usual 30 days or added to Cheshvan’s usual 29 days. Thus, a Jewish year or leap year can have 353/383, 354/384, or 355/385 days.

These are called deficient, regular, and complete years respectively, and which type a Jewish year will be is determined using the number of days between two Rosh Hashana observations (actual or predicted).

Solved Example

Example 1

John was born on January 1, 1950, at 2 pm. What would be his birthday on the Jewish calendar, given that 1950 was a non-intercalated, deficient Jewish year, and Rosh Hashana occurred on September 24, 1949?

Solution

The year 1950 is equivalent to the Jewish year 1950 A.D. + 3760 = 5710 A.M. (Anno Mundi) since it comes before Rosh Hashana (start of the Jewish year) in 1950. Here, we do not require the leap year information because the month of Adar is not involved.

Given that September 24, 1949 AD was Tishri 1 (Rosh Hashana), then:

  • Tishri 1–30 = Sep 24 – Oct 23
  • Cheshvan 1–29 = Oct 24 – Nov 21
  • Kislev 1–29 (DEFICIENT) = Nov 22 – Dec 19
  • Tevet 1–29 = Dec 20 – Jan 17

Since the person was born on Jan 1 and December is 31 days long, Jan 1 before sunset (2 pm) would be the 12th day of Tevet. Hence, the Jewish birthday of John is Tevet 12, 5710 A.M.

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